The present invention relates to an inkjet head for an inkjet printing apparatus.
Recently, inkjet printing apparatuses are widely used. An inkjet head (i.e., a printing head) employed in an inkjet printing apparatus is configured such that ink is supplied from an ink tank into manifolds and distributed to a plurality of pressure chambers defined in the inkjet head. By selectively applying pressure to the pressure chambers, ink is selectively ejected through the nozzles, which are defined corresponding to the pressure chambers, respectively. For selectively applying pressure to respective pressure chambers, an actuator unit composed of laminated sheets of piezoelectric ceramic is widely used.
An example of such an inkjet head is disclosed in U.S. Pat. No. 5,402,159, teachings of which are incorporated herein by reference. The above-described patent discloses an inkjet head which includes an actuator unit having ceramic layers which are consecutive laminated planes extending over a plurality of pressure chambers. In the inkjet head of the above-mentioned patent, the piezoelectric ceramic layers of the actuator unit generally include active layers and inactive layers. The active layers are located at the pressure chamber side and sandwiched between a common electrode kept at a ground potential and driving electrodes (individual electrodes) respectively located at places corresponding to the pressure chambers. The inactive layers are located on a side opposite to the pressure chambers and are not provided with electrodes. By selectively controlling the potential of the driving electrodes to be different from that of the common electrodes, the active layers expand/contract in the stacked direction of the layers in accordance with a piezoelectric longitudinal effect. With this expansion/contraction of the active layers, the volume within the corresponding pressure chambers varies, thereby ink being selectively ejected from the pressure chambers. The inactive layers deform very little and serve to support the active layers from above so that the active layers effectively expand/contract in the stacked direction of the layers.
Recently, there is a great demand for highly integrated pressure chambers. However, the inkjet head of the type as described in the above-mentioned patent is insufficient to meet such a demand.
In view of the above, the present invention is advantageous in that an inkjet head having highly integrated pressure chambers is provided.
According to an aspect of the invention, there is provided an inkjet head, which is provided with a plurality of pressure chambers, each of which being configured such that an end thereof is connected to a discharging nozzle and the other end is connected to an ink supplier, and an actuator unit for the plurality of pressure chambers. Specifically, the actuator unit includes a plurality of inactive layers and at least one active layer, both made of piezoelectric material. The plurality of inactive layers are arranged on a pressure chamber side to cover the plurality of pressure chambers. The at least one active layer is arranged on an opposite side of the pressure chambers with respect to the inactive layers. In an embodiment, the active layer is segmented to a plurality of segments which are located at positions correspond to the plurality of pressure chambers. Further, each segment of the active layer is sandwiched between a common electrode and a driving electrode.
Optionally, when a driving electrode provided on a segment of the active layer is set to have a voltage different from the potential of the common electrode, the segment of the active layer deforms in accordance with piezoelectric transverse effect. In this case, a unimorph effect is generated by the deformation of the segment of the active layer in association with the inactive layers to vary a volume of the pressure chamber corresponding to the segment.
Optionally, at least one layer includes a plurality of active layers.
Further optionally, an electrode arranged farthest from the pressure chamber may be configured to be the thinnest electrode between the common electrode and the driving electrode.
In an embodiment of the invention, an electrode closest to the pressure chamber is the common electrode.
In a particular case, a thickness of each of the at least one active layer is 20 xcexcm or less.
In an embodiment, condition:
t/Txe2x89xa60.8
is satisfied,
wherein, t represents a thickness of the active layer, and T represents the entire thickness of the active layer and the inactive layers. More preferably, t/T may be 0.7 or less.
Further, conditions:
0.1 mm xe2x89xa6L0xe2x89xa61 mm,
and
0.3xe2x89xa6xcex4L0xe2x89xa61,
may be satisfied,
wherein L0 represents a width of the active layer in a shorter side, and
wherein xcex4 represents a width of a driving electrode in a direction similar to the width L of the active layer.
Still optionally, all of the at least one active layer and the at least one inactive layer may be formed of the same material.
Optionally or alternatively, all of the at least one active layer and the inactive layers have substantially the same thickness.
In an embodiment, the number of the active layer and the number of the inactive layers are one and two, respectively. Alternatively, the number of the active layers and the number of the inactive layers can be two and two, respectively.
Still optionally, the common electrode may be kept to a ground potential.
According to another aspect of the invention, there is provided an inkjet head, which is provided with a plurality of pressure chambers, each of which being configured such that an end thereof is connected to a discharging nozzle and the other and is connected to an ink supplier, and an actuator unit for the plurality of pressure chambers. Further, the actuator unit includes a plurality of inactive layers arranged on a pressure chamber side and formed of piezoelectric material and at least one active layer arranged on an opposite side of the pressure chambers with respect to the inactive layers and formed of piezoelectric material, the plurality of inactive layers being arranged to cover the plurality of pressure chambers, the at least one active layer being segmented to locate at positions corresponding to the plurality of pressure chambers. Furthermore, each segment of the at least one active layer is sandwiched between a common electrode and a driving electrode, and each segment of the at least one active layer sandwiched between the common electrode and the driving electrode deforms in accordance with piezoelectric transverse deformation effect so that the each segment performs unimorph deformation in accordance with a voltage applied to each of the driving electrode. Optionally, the common electrode may be kept to a ground potential.